The secret center to these 3D printed metal objects

3D printers are becoming familiar objects to even those not obsessed with technology, perhaps in part because of the kerfuffle over a certain blueprint allowing for the creation of a gun but also because they are interesting enough to capture anyone's imagination. 3D printing using metal is the obvious next step but as liquefying metal tends to create a rather dangerous environment developers have had to come up with new ideas. At Hack a Day you can read about a project that has been printing metal globes and wires using a mixture of 75% gallium and 25% indium which is liquid at room temperature and quickly oxidizes a shell when exposed to air. Perhaps not the most solid of construction materials but a very interesting step towards home 3D printing with metal.

"While 3D printers of today are basically limited to plastics and resins, the holy grail of desktop fabrication is printing with metal. While we won’t be printing out steel objects on a desktop printer just yet, [Collin Ladd], [Ju-Hee So], [John Muth], and [Michael D. Dickey] from North Carolina State University are slowly working up to that by printing objects with tiny spheres of liquid metal."

It's typically done using a technology called Direct Metal Laser Sintering(DMLS), which uses a laser to sinter powdered metal into solid shapes of incredibly complex geometries.

It can be used with many different metals, including superalloys, and can produce metal parts that are as strong as forged in some cases.

It's starting to be used in race engines, which is where I first heard about it. The technology can make metal objects in shapes that would otherwise be impossible to cast or forge, with little to no machining afterward.